The invention relates to a method of preparation of diorganosilanes by disproportionation of a hydridosiloxane comprising at least one terminal SiH group and at least one siloxane bond in the presence of Lewis acid catalysts. The invention also relates to oligosiloxanes that are produced as byproducts of the above reaction.
Two methods that are typically used for synthesis of siloxane oligomers and polymers are ring opening polymerization of cyclic siloxanes and polycondensation. The polycondensation reaction between functional silanes or oligosiloxanes leads to the formation of siloxane bond and elimination of a low molecular weight byproduct. The polycondensation of low molecular weight siloxanol oils is the most common method for synthesis of polysiloxanes that produces water as a byproduct. Other non-hydrolytic condensation reactions can also be used that result in different byproducts (see for example United States Patent Application US2004/0127668 A1). Most of these condensation reactions require the presence of a catalyst. Recently it has been reported that organo-boron compounds are extremely efficient catalysts for the reaction between hydrosilanes and silanols (WO 01/74938 A1) producing hydrogen as a byproduct.
Hydrosilanes and organo-boron compounds are also well known as excellent reducing agents for aldehydes, ketones, esters, imines and other functions. These systems are also able to reduce alcohols in a two-step reaction. First, the silylation of alcohol occurs leading to the formation of alkoxysilane, which in the second step is cleaved producing a hydrocarbon and a disiloxane. The SiOC bond cleavage by silyl hydrides in the presence of Lewis acid catalyst like B(C6F5)3 in many cases occurs quantitatively and so fast that it can be used for the synthesis of polysiloxanes (US2004/0127668 A1). This method of preparation of polysiloxanes may be very attractive as the substrates bearing the SiOR and SiH groups are often commercially available, inexpensive and easy to handle. The byproduct of this condensation is a hydrocarbon and the reaction occurs rapidly under mild conditions.
Diorganosilanes, R1R2SiH2 are typically made by the reduction of dichlorosilanes in the presence of strong reducing agents, which are expensive and very hazardous to handle. These compounds find use in electronic materials, semiconductors, integrated circuits and are useful intermediates for the preparation of novel siloxane and organosilicone copolymers as well as small molecules, such as silahydrocarbons. Dimethylsilane (Me2SiH2) and trimethylsilane (Me3SiH) are also important substrates for low K dielectric coatings made using chemical vapor deposition (CVD) techniques. Methods for generating diorganosilanes on-demand under safe and convenient conditions are therefore highly desirable.